'Device or resource busy' error

[luckypoem]

root@RegalMusty-VM:~/udptunnel-by-astroza# ls LICENSE README.md include server.c tun.c Makefile client.c scripts socket.c util.c root@RegalMusty-VM:~/udptunnel-by-astroza# make gcc -Wall -I./include -c socket.c gcc -Wall -I./include -c tun.c gcc -Wall -I./include -c util.c gcc -Wall -I./include -c client.c gcc -Wall -I./include -c server.c gcc socket.o tun.o util.o client.o -o client gcc socket.o tun.o util.o server.o -o server root@RegalMusty-VM:~/udptunnel-by-astroza# ls LICENSE client include server.c socket.o util.c Makefile client.c scripts server.o tun.c util.o README.md client.o server socket.c tun.o root@RegalMusty-VM:~/udptunnel-by-astroza# ./server 53 my-password perror: Device or resource busy root@RegalMusty-VM:~/udptunnel-by-astroza#

how to fix it?

[Filius-Patris]

There's already a process listening on port 53 probably. Use ss -l | grep 53 to see if this is the case.

[peacand]

Or you may have already a tun0 interface (it was my case). You can check with "ifconfig". If you see a tun0 interface, then you need to change every "tun0" into "tun1" or "tun2" in this repo (C code + shell scripts)